DE102016203260A1 - Method for starting an internal combustion engine of a hybrid vehicle and control unit for operating the method - Google Patents

Abstract

The invention relates to a method for starting an internal combustion engine of a drive train in a hybrid vehicle having at least one internal combustion engine and at least one electric motor as a drive unit in a parallel hybrid arrangement, in particular a so-called P2 arrangement.

Description

State of the art

The invention relates to a method for starting an internal combustion engine of a drive train in a hybrid vehicle having at least one internal combustion engine and at least one electric motor as a drive unit in a parallel hybrid arrangement, in particular a so-called P2 arrangement.

The core of the invention is to improve the controllability during operation of the hybrid vehicle in a purely electrical mode, and to design the combustion engine such that at least two different starting process requirements are met. On the one hand, this is a so-called comfort start, which places the driver's comfortable start procedure at the expense of the start time in the foreground. On the other hand, a quick start is to be possible, which emphasizes the brevity and efficiency of the starting process at the expense of his comfort for the driver.

In order to start an internal combustion engine, it must be accelerated to a minimum start speed, in order then to be able to start it by means of fuel supply and ignition. To start the engine, the intended for the engine start electric machine must apply the necessary starting torque. If the internal combustion engine of a hybrid vehicle is started during the electric driving operation, the engine start can impair the electric driving operation in such a way that part of the electrically available energy is used for the engine start and consequently the energy that can be used for the drive suffers losses.

A parallel hybrid arrangement is known in a so-called P2 arrangement of an electric motor at the transmission input, wherein this is separated by a clutch from the internal combustion engine. For an internal combustion engine start from the purely electric driving operation different operating strategies are known in this arrangement.

When the engine is started, there is generally a great deal of blurring in determining the current engine torque acting on the wheels. It is therefore always unclear how much moment the internal combustion engine is currently producing. This determination becomes all the more difficult in dynamic states, so that the problem of known starting strategies generally consists in the fact that the transition from the purely electric drive to the hybrid drive, ie the start of the internal combustion engine while driving, is sometimes clearly perceived by the driver, also by deviations from the driver's request moment.

The object of the invention is therefore to maintain the desired moment requested by the driver during the engine start, thereby simplifying the control. In this case, at least two different start procedures should be feasible, with a first start sequence puts the ride comfort in the foreground and a second start process aimed at a speedy implementation of increased desired torque.

Disclosure of the invention

This problem is solved by reducing the uncertainty around the knowledge of the current engine torque, or by losing influence on the dynamics. For this purpose, an operating point of the internal combustion engine is determined, which the internal combustion engine can reach quickly in order to bring as little dynamics into the engine start. Since the moment of the electric motor can be determined much more accurately even in dynamic operating states, the center of gravity of the control is shifted to the regulation of the electric motor torque, so that the wheel torque during the starting process becomes so controllable that it corresponds exactly to the driver's desired torque. Thus, the driver's desired torque is ensured via the coupling between the electric motor and transmission. The better the moments are regulated, the faster and more comfortable the engine start will be. At the end of the engine start, during synchronization, it is important that the driver's desired torque is hit pretty precisely to allow a comfortable and fast synchronization.

The object is further achieved by adapting the starting strategy to the respective driving situation. On the basis of the boundary conditions, such as the driver's desired torque or position and the gradient of the accelerator pedal, a distinction is made between at least one comfort start and one quick start. Thus, if the driver, for example, fully penetrates the accelerator pedal, for example, for a speedy overtaking, then the method of the invention selects the quick start. But if the position of the accelerator pedal remains constant and the engine start, for example, because the state of charge of the battery drops below a certain value, then the comfort start is selected because the longer startup time is not a problem due to lack of strong acceleration request.

The invention is realized in a parallel hybrid drive system in which a first clutch, the so-called K0 clutch, is located between the internal combustion engine and the electric motor. Between the electric motor and a Gearbox is a second clutch, the so-called K1 / 2 clutch. The inventive method can be realized with each gear, the clutch capacity can be controlled. This is also a dual-clutch transmission or an automated manual transmission into consideration. It is only important that the capacity of the coupling can be specified or adjusted.

The present invention initially relates to a method for starting an internal combustion engine within a drive train of a hybrid vehicle.

It is essential to the invention with regard to the internal combustion engine control that the internal combustion engine is constantly driven during the entire starting phase with a moment during which no turbocharger is still active.

This is generally the case for a pure suction motor, but can also be done particularly effectively in a turbo engine when the engine is driven with maximum suction torque. Suction moment is the engine torque in which the turbocharger is not yet working. This suction torque can be provided by the engine very quickly and constantly available and is thus much more reliable determinable than the moment under operation of the turbocharger.

The implementation of the present invention is expressly not limited to an arrangement with a turbo engine but also includes a suction motor. In particular, arrangements with a diesel engine or gas engine for implementing the method according to the invention are conceivable.

The synchronization of the two drive units is ensured only via the K0 coupling. A resulting increase in slip (at a constant engine torque) must be prevented by means of a slip controller and thus by reducing the electric motor torque: The engine torque is kept deliberately constant during synchronization. Thus, to keep the slip constant while the K0 clutch closes and, accordingly, the two moments of combustion engine and electric motor add together, the slip controller reduces the torque of the electric motor.

A control unit HCU (Hybrid Control Unit) controls the slip via a slip control, which sets the electric motor torque so that a setpoint slip is established or kept constant. The nominal slip is understood as a constant adjustment parameter that is defined by application. The smaller he is, the better this is basically. However, it is not always possible to apply the slippage too small.

The TCU sets the clutch torque of the K1 / 2 in this particular slip mode to the driver's desired torque and ignores the current engine torque.

In a further embodiment of the invention, the method has two starting variations: two different engine starting variants may be selected based on certain engine start trigger conditions, such as an accelerator pedal threshold or accelerator pedal gradient threshold (eg, during an overtaking operation for which the driver accelerates rapidly). A so-called comfort start puts the emphasis on comfortable engine starting behavior at the expense of the starting time. A so-called quick start, however, puts the start time and thus a fast torque build-up of the drive units in the foreground. This is done at the expense of comfort.

The torque transfer after the start takes place in such a way that the desired torque of the internal combustion engine is calculated from the driver's desired torque. The torque of the internal combustion engine follows the desired torque inert, from which the desired torque of the electric motor is calculated from (driver request torque minus current moment of the internal combustion engine)

The present invention further relates to a control unit for operating the method according to the invention. The control unit is used for signal transmission between the individual components of the drive train and their control based on the transmitted signals. This can be a separate control unit. However, this task can also be integrated in an engine control unit or in a transmission control unit.

Embodiments of the invention are illustrated in the figures and explained in more detail in the following description. It shows

1 a powertrain of a hybrid vehicle in parallel design - a so-called P2 arrangement

2 a diagram with speeds and torques for the comfort start

3 a diagram with speeds and torques for the quick start

1 schematically shows a drive train of a hybrid vehicle in parallel construction. Between the combustion engine 11 and the electric motor 12 there is a first clutch K0 13 which is open in the presentation. The electric motor rotates at a speed n _EM , whereas the internal combustion engine is out of service and is also not being towed, whose speed n _V is therefore equal to zero. Between electric motor 12 and the transmission 15 , indicated here as a dual-clutch transmission, there is a second clutch K1 / 2 14 ,

Also shown is a signal transmission device HCU 16 (Hybrid Control Unit), so an additional control unit which controls the components of the drive train in hybrid vehicles and thus controls the inventive method.

This task can take over with appropriate technical design, the engine control unit or the transmission control unit. The HCU 16 communicates by means of signal transmission with the aggregates 11 . 12 . 13 . 14 . 15 and thus can exchange data and control commands and execute the method according to the invention.

2 shows a method for starting the internal combustion engine in the hybrid vehicle in comfort mode. Shown schematically is a diagram with rotational speeds and torques over time for a comfort start, wherein the time rail is schematically divided into phases. The numbering of phases 1 to 6 correlates with the corresponding steps S1 to S6 to be carried out during the phases. A method step can have several sub-steps, as will be explained below. Shown are the speed of the internal combustion engine n _V ( 111 ), the speed of the electric motor n _EM ( 112 ), the torque of the internal combustion engine M _V ( 211 ) and the torque of the electric motor M _EM ( 212 ). Further curves represent the different clutch torques and thus their subsequent shift possibilities in a closed, opened or slipping mode. These are the clutch torque M _K0 ( 213 ) the K0 and the clutch torque M _{K1 / 2} ( 214 ) of the K1 / 2.

Also shown is the transmission input speed ( 100 ), which should remain constant, unless a change is required by the driver, and the driver's desired torque ( 200 ), which should remain constant unless a change is requested by the driver.

In phase 1, the conditions for the starting driving operation, namely a purely electric operation of the hybrid vehicle is provided, so that the electric motor with the rotational speed n _EM ( 112 ) and clutch K0 is open and the engine is out of operation. Since the clutch K1 / 2 is closed, n _EM ( 112 ) also the transmission input speed ( 100 ). Phase 1 thus goes from the arrangement in 1 out.

Phase 1 describes the starting point for the method according to the invention and can therefore take a long time - depending on how long purely electric driving is desired and the state of charge of the battery is possible. In principle, phase 1 can therefore last several hours or days before an engine start is triggered. The time of the engine start, and thus the end of phase 1 is the beginning of phase 2 and thus the beginning of the inventive method. This beginning is triggered by conditions such as falling below a state of charge of the battery or the trigger conditions for a quick start. Also, the driver selectable operating conditions in which an engine operation can be suppressed or preferred can have an influence on this.

Phase 2 starts the process according to the invention. Phase 2 starts with an increase in n _EM ( 112 ). A control unit sets the clutch torque M _{K1 / 2} ( 214 ) in this phase to the driver's desired torque 200 , To the transmission input speed ( 100 ), the K1 / 2 is gradually switched to a slip mode. This corresponds to a continuous lowering of the clutch torque M _{K1 / 2} . In the 2 shown curve shows only a schematic lowering of the clutch torque.

Phase 3a begins with the previously open K0 being closed with a defined moment. The target torque depends on the drag torque of the internal combustion engine. At the same time M _{EM is} equally increased, whereby n _EM remains constant. The combustion engine is towed by the K0 torque.

The target value of the engine torque Mv is now set to a constant value and not changed during the rest of the engine start phase. The setpoint torque is defined by the maximum torque of the internal combustion engine in which the turbocharger is not or only insignificantly works (hereinafter referred to as "suction torque"). The towing of the internal combustion engine is then at least until a minimum _speed n _Vstart for starting the internal combustion engine is reached.

This is followed by the actual engine start with subsequent synchronization of the speeds n _EM and n _{V of} the two drive units:
After the ignition or the starting of the internal combustion engine, the K0 is again completely open, so that the internal combustion engine, or its torque initially does not act on the transmission input.

The exact time of the first injection and thus the first ignition of the internal combustion engine is determined by an engine control unit (ECU). At the beginning of phase 3a, therefore, an injection release to the engine control unit takes place. From this point in time, the internal combustion engine will start injectioning provided all boundary conditions, such as synchronization between camshaft and crankshaft or starting rpm, are met. It may also be that the K0 is not yet reopened, even though the engine is already injecting.

An embodiment of the inventive method for the comfort start is based, inter alia, that the (re) opening the K0 triggered only by _V n. The speed n _{V of} the internal combustion engine is subsequently increased to a speed n _Vcomf which is suitable for initiating the synchronization of the internal combustion engine and the electric motor under the conditions provided for the comfort start. This n _Vcomf is above the n _EM , but should not be too big.

As soon as the engine speed nV is above the transmission input speed plus a parameterizable offset, the K0 clutch is started to close.

The HCU controls the slip of the K0 via a slip control, the M _EM ( 212 ) so that the target slip is built up or kept constant. M _V ( 211 ) remains constant at said suction moment.

The clutch torque M _{K1 / 2} ( 214 ) remains at the driver's request torque in this phase 200 and ignores the current engine torque M _EM ( 212 ) and M _V ( 211 ). This ensures that the vehicle does not unintentionally accelerate during engine startup.

Subsequently, with the beginning of phase 4, the clutch torque M _K0 ( 213 ) continuously raised until the K0 is closed again. Thus, the synchronization between electric motor and combustion engine is ensured exclusively via the K0. A resulting increase in slip must be controlled by the slip control on the HCU and thus by reducing the M _EM ( 212 ) be prevented.

By reopening the K0 in the meantime, the emphasis is clearly on a comfortable engine start-up behavior at the expense of the start time. (The following in 3 On the other hand, the quick start shown places emphasis on the start time and thus a quick build-up of torque - again at the expense of comfort.)

With achieved synchronization of the speeds n _EM and n _V also the K0 will be completely closed at the beginning of phase 5. The hitherto in slip mode K1 / 2 is not further on the driver's desired torque 200 set and is now also gradually closed, or their clutch torque M _{K1 / 2} continuously raised until the engine speeds 111 and 112 with the transmission input speed 100 is synchronized.

In the subsequent phase 6, the speeds of internal combustion engine, electric motor and transmission input are synchronous. Both clutches are closed. It follows a torque transfer among the drive units such that the desired torque of the engine from the driver's desired torque 200 is calculated. M _V ( 211 ) follows the setpoint momentum, from which M _EM ( 212 calculated as [driver's request torque minus M _V ( 211 )]. In accordance with an increase in the torque of the internal combustion engine, the torque of the electric motor decreases.

In a higher order, the phases 3b and 4 can be understood together as a synchronization phase or as a start and synchronization phase and thus the method _{steps can be} summarized as S _sync . During this process, the detailed sequence of the method steps realizes the distinction between the comfort start and the quick start. In general, one can summarize this synchronization phase or start and synchronization phase as the starting of the internal combustion engine, increasing its speed to a suitable for synchronization speed, which is above the speed of the electric motor.

3 shows a method for starting the internal combustion engine in the hybrid vehicle in the quick start mode. The nomenclature of the representation corresponds to that of 2 , The procedure differs in the course of the in 2 Illustrated method in phases 3b 'and 4' as follows:

Again, with the ignition or the starting of the internal combustion engine begins the phase 3b or 3b '. For the quick start, the K0 is not opened, but their clutch torque M _K0 increased significantly. This is triggered (as the reopening of K0 at the comfort start) only by n _V.

Thus, in the phase 3b 'already affects the torque of the engine with the transmission input.

The speed n _{V of} the internal combustion engine is increased so far to a speed n _Vfast , which is suitable to initiate the synchronization of the internal combustion engine and electric motor under the conditions provided for the quick start. In contrast to the comfort start, this n _{Vfast can} already be below the n _EM , so that it can be synchronized earlier. The phase 3b 'is in reality therefore much shorter than the phase 3b of the comfort start.

Subsequently, the K0 is closed further at the beginning of the phase 4 ', whereby the phase 4' is significantly shorter than the phase 4, since the moment difference until the complete closing of the K0 is significantly smaller than the comfort start.

LIST OF REFERENCE NUMBERS

1

 powertrain

11

 internal combustion engine

12

 electric motor

13

Coupling K0

14

 Coupling K1 / 2

15

 transmission

16

 control unit

100

 Transmission input speed

111

Speed n _{V of} the internal combustion engine

112

Speed n _{EM of} the electric motor

200

 Driver input torque

211

Torque of the internal combustion engine M _V

212

Torque of the electric motor M _EM

213

Clutch torque M _K0

214

Clutch torque M _{K1 / 2}

Claims (10)

Method for starting an internal combustion engine ( 11 ) of a drive train ( 1 ) of a hybrid vehicle, the drive train comprising at least - the internal combustion engine ( 11 ), which is at speed n _V ( 111 ) and with torque M _V ( 211 ) can be operated and at n _V ≥ n _Vstart can be started, - an electric motor ( 12 ), which is at speed n _EM ( 112 ) and with torque M _EM ( 212 ), - a transmission ( 15 ), - one between combustion engine ( 11 ) and electric motor ( 12 ) arranged coupling K0 ( 13 ), which with a clutch torque M _K0 ( 213 ) opened with M _K0 ( 213 ) = 0, closed with M _K0 ( 213 ) = M _K0max or in a slip mode with M _K0 ( 213 ) = M _K0slip can be switched, - one between electric motor ( 12 ) and gearboxes ( 15 ) arranged clutch K1 / 2 ( 14 ), which with a clutch torque M _{K1 / 2} ( 214 ) opened in with M _{K1 / 2} ( 214 ) = 0, closed with M _{K1 / 2} ( 214 ) = M _{K1 / 2max} or in a slip mode with M _{K1 / 2} ( 214 ) = M _{K1 / 2slip} can be connected, wherein the drive train is at the beginning of the process in a purely electric driving mode with M _K0 = 0 and M _{K1 / 2} = M _{K1 / 2max} and n _EM > 0, comprising at least the method _steps S2 : Increase of n _EM ( 112 ) Lowering the M _{K1 / 2} ( 214 ) on M _{K1 / 2slip} S3a: increasing the M _K0 ( 213 ) on M _K0slip setting the M _{K1 / 2} ( 214 ) to a driver request torque ( 200 ) at n _V ≥ n _Vstart : S _sync : starting the internal combustion engine ( 11 ) Setting the M _V ( 211 ) at a predetermined value, increasing the n _V ( 111 ) on n _Vsyncstart with n _Vsyncstart > n _EM Increase the M _K0 ( 213 ) to M _K0max Reduce the M _EM at n _EM = n _V : S5: Increase the M _{K1 / 2} ( 214 ) on M _{K1 / 2max} The method of claim 1, further comprising the step S6: calculating a setpoint value of the M _V ( 211 ) from driver request torque ( 200 ) Calculating a setpoint of the M _EM ( 212 ) as driver request torque minus M _V ( 211 ). Method according to claim 1 or 2, wherein the method step S _{sync has the} following overall substeps: S3b: starting the internal combustion engine ( 11 ) Setting the M _V ( 211 ) at a predetermined value lowering the M _K0 to 0 increasing the n _V ( 111 ) on n _Vsyncstart with n _Vsyncstart = n _Vcomf > n _EM on reaching n _V = n _Vsyncstart : S4: increasing the M _K0 ( 213 ) to M _K0max Reduce the M _EM Method according to claim 1 or 2, wherein the method step S _{sync has the} following overall substeps: S3b ': Starting the internal combustion engine ( 11 ) Setting the M _V ( 211 ) at a predetermined value increasing M _K0 increasing the n _V ( 111 ) on n _Vsyncstart with n _Vsyncstart = n _Vfast <n _EM on reaching n _V = n _Vsyncstart : S4 Increase the M _K0 ( 213 ) to M _K0max Reduce the M _EM Method according to claim 3 or 4, wherein for S4 increasing M _K0 ( 213 ) continuously. Method according to one of claims 3 to 5, wherein for S2 the sinking of the M _{K1 / 2} ( 214 ) continuously on M _{K1 / 2slip} . Method according to one of claims 3 to 6, wherein for S5 increasing the M _{K1 / 2} ( 214 ) continuously on M _{K1 / 2max} . Method according to one of claims 1 to 7, wherein the setting of the Mv takes place on a predetermined value M _sucker , which corresponds to the maximum torque at which the internal combustion engine operates without a turbocharger. Control device for carrying out the method according to one of claims 1 to 8. Drive train for a hybrid vehicle, comprising at least one internal combustion engine ( 11 ), which is at speed n _V ( 111 ) and with torque M _V ( 211 ) can be operated and at n _V ≥ n _Vstart can be started, - an electric motor ( 12 ), which is at speed n _EM ( 112 ) and with torque M _EM ( 212 ), - a transmission ( 15 ), - one between combustion engine ( 11 ) and electric motor ( 12 ) arranged coupling K0 ( 13 ), which with a clutch torque M _K0 ( 213 ) opened with M _K0 ( 213 ) = 0, closed with M _K0 ( 213 ) = M _K0max or in a slip mode with M _K0 ( 213 ) = M _K0slip can be switched, - one between electric motor ( 12 ) and gearboxes ( 15 ) arranged clutch K1 / 2 ( 14 ), which with a clutch torque M _{K1 / 2} ( 214 ) opened in with M _{K1 / 2} ( 214 ) = 0, closed with M _{K1 / 2} ( 214 ) = M _{K1 / 2max} or in a slip mode with M _{K1 / 2} ( 214 ) = M _{K1 / 2slip} can be connected, wherein the drive train is at the beginning of the process in a purely electric driving mode with M _K0 = 0 and M _{K1 / 2} = M _{K1 / 2max} and n _EM > 0, and a control _device for implementation The method according to any one of claims 1 to 8.

Images